Category: Chemistry Notes PPT

Zinc is one of the transition earth metals which has a lustrous bluish-white colour. The zinc symbol is represented as Zn.  The Zn atomic number is 30. The abundance of the zinc element is estimated at almost 65 grams for every ton of the Earth’s crust. The word ‘zinc’ has a German origin whereas its exact derivation goes beyond the Persian word ‘sing,’ which means stone.

Zn in chemistry is a very important element and has several chemical properties.

Zn + 2HCl → ZnCl2 + H2 

2Zn + O2 → 2ZnO

• Zinc consist of five different natural stable isotopes

• These isotopes include; 64Zn, 66Zn, 67Zn, 68Zn and 70Zn

• Zinc has the lowest melting point after Cadmium and Mercury among all the  transition metals

• Zinc does not react with water directly. However, metallic zinc can react with oxygen present in the air in the presence of water vapour and thus, form zinc hydroxide.

Zn + 2H2O → Zn(OH)2 + H2

Chemical Properties of Zinc

Uses of Zinc

Zinc is one of the heavily used metals within the industry. Here is a list of some of the applications of zinc:

• The majority of the zinc is used in the manufacturing of zinc oxides as well as creating roofing materials

• Zinc oxides are mainly used as an additive to rubbers for the production of tires. This helps to withstand higher temperature as well as prevent any unnecessary wear and tear

• Zinc is also used in galvanizing other metals such as iron and steel. It prevents iron from rusting. On the other hand, galvanized steel is mainly used in manufacturing vehicles

• Alloys of metals are also formed using zinc. Some of the examples include nickel silver, brass, and even aluminium solder

• Zinc is also used in the production of die-casting. It plays an integral part in electronic hardware.

• Zinc oxide has also found its way into cosmetics, inks, pharmaceuticals, and even plastics

• Zinc sulfide is used for making fluorescent lights, x-ray screens as well as luminous paints

 Biological Significance of Zinc

The zinc atomic structure plays an integral role in every other living organism. In fact, almost 20 metalloenzymes have an active site formed through zinc. About 2.5g of zinc is present in an average human body, whereas we consume almost 15 milligrams per day. Some of the most common sources of zinc in food include beef, lamb, sunflower seeds, herrings and cheese.

On the contrary, zinc has carcinogenic properties too. Inhaling zinc (II) oxide can cause ‘zinc chills’ or commonly known as ‘oxide shakes.’

Physical properties of Zinc

Some of the most astounding physical properties of zinc include:

• At normal room temperature, it remains brittle with a crystalline state

• One of the properties of zinc is that when heated between 110oC to 150oC, it becomes malleable and ductile

• Zinc is highly reactive with dilute acids causing the release of hydrogen

• Zinc also shows its reactive properties while combing with oxygen or any other non-metal

Most Common Zinc Compounds

It is imperative to understand that the majority of the zinc compounds are widely used in organic synthesis. Below is a list of some of the most widely used zinc compounds:

• Zinc halogenides (fluoride, bromide, chloride, iodide)

• Zinc carbides

• Phosphides

• Sulfite, selenide, zinc arsenide

• Thiocyanates, cyanides and thiosulfates

• Ammonia complexes

• Hydroxo-zincates: amphoteric compounds formed from hydroxide and zinc oxide

 Interesting Facts about Zn Element

Here is a list of some of the most interesting facts about zinc that are worth mentioning:

• The 24th most common element that one can find on Earth’s crust is zinc

• Zinc contributes to almost 0.0075% of the entire Earth’s crust

• Zinc is also available in seawater, although it’s about 30 parts per billion

• The first known use of zinc dates back to 1000 BC

• The majority of the zinc (95%) are mined within ore deposits of sulfide

• Zinc is the fourth most commonly used metal within the industry

• Current zinc production includes 70:30; mining and recycling ration

• In 1746, Marggraf defined the zinc atomic structure while proclaiming it has a distinct element

The pH Of Various Substances?

Chemistry has three major classifications as acids and bases. These are the essential elements of chemistry to carry out reactions and form water and salt. In our daily life, we use different compounds that are either acids or bases. Daily life examples are milk turning sour into curd because of the presence of lactic acid. It all depends upon the pH of various substances. 

How To Define Acids And Bases?

The two chemical compounds: acids and bases have different definitions according to different people. Arrhenius defined both of them as the ionizing compounds and differentiated acids and bases as:

Arrhenius Theory Of Acids And Bases

According to Arrhenius’s theory, when we dissolve a compound in aqueous solution, it releases some ions. Thus he defines his theory on acids and bases. 

Acids: Acids leave H+ ions when dissolved in the solution or water. Further, these ions form H3O+ or hydronium ions when combined with water molecules. 

Bases: Bases are the compounds when dissolved in water leaves OH– ions in the solution.  

Here is the reaction explaining chemical equation of formation of hydronium ions:

HCl(aq)  -> H+ (aq) + Cl–(aq)

In the above reaction, when HCl is dissolved in the aqueous solution, it forms H+ ions. Further, these H+ ions dissolve to form H3O+ ions.

HCl(aq) + H2O(l) -> H3– (aq) + Cl– (aq)

The reaction of base dissolving in water:

NaOH (aq)  -> Na+ (aq) + OH–  (aq)

Acids And Bases- pH Scale

Based on the concentration of hydrogen ions, solutions are classified as basic or acidic. Acidic solutions are the one, which has a higher H+ concentration as compared to water. However, basic solutions are the one, which has lower H+ concentration. The concentration of Hydrogen ion is expressed pH that is calculated as:

pH = -log10 [H+]

The square brackets around the hydrogen ion state the concentration. The concentration of H+ in water is 1×10-7 M, which is the value of 7.0 (neutral pH). However, the concentration of H+ moves away whenever an acid or base is added to a water-based solution. 

In terms of pH, an acid in chemistry is a compound that enhances the concentration of H+ in the solution. In contrast, a base provides OH– ion that combines with H+ and removes them from the solution. As a result, bases are the substances, which increase the pH value, and acids are the substances that decrease the pH value.

The pH scale is generally used to rank the solutions in terms of alkalinity (basicity) and acidity. It ranges from 0 to 14, and most of the solutions fall in this range. 

(Image to be added soon)

The above picture shows that anything below 7.0 in pH scale is acidic, and above 7.0 is basic. 

What pH Values Correspond To Acids And Bases?

Strong Acids:

Generally, acids are substances with a pH value of less than 7.0. The value goes on decreasing as the amount of H+ ion increases in the solution. Strong acids are the substances that release H+ ions rapidly or that are 100% ionizable in the solution. Thus, the strong acids have less pH value, nearly 0 to 1. The lower the pH value, the higher is the concentration of H+ ions in the solution, and hence, stronger is the acid. 

For example,

HCl (aq) -> H+ (aq) + Cl– (aq)

It shows that hydrogen chloride, when dissolved in solution, splits out to give hydrogen and chloride ions. Some other examples of strong acids include hydrobromic acids (HBr), sulphuric acid (H2SO4), and many more.

Strong Bases 

The pH of various substances decides its nature. However, bases are substances with pH values greater than 7.0. The value goes on increasing as the amount of H+ decreases in the solution. Strong bases are those substances that release OH– ion in the solution rapidly. These ions scoop the H+ ion present in the solution, and as a result, increase the pH value of the solution. Thus, strong bases usually have pH values, approximately 13 or 14. 

For example, sodium hydroxide (NaOH) is the strong base that splits in the aqueous solution to produce sodium ion and hydroxide ion. Some other examples of strong bases include potassium hydroxide (KOH), and hydroxides of alkali metals.

Weak Acids

A weak acid is the one that fails to ionize in the solution completely. It releases H+ ion in the low concentrations, and thus pH ranges from 5 to 7. Some of the examples include formic acid (HCOOH), acetic acid (CH3COOH), and many more.

Weak Bases

Weak bases are the substances that do not undergo complete dissociation. As a result, there is a decrease in OH– ion concentration and an increase in pH value. Some of the examples include methylamine and ammonia. 

The mole is a measure or the base unit for the amount of substance present in the given sample. 1 mole is a number that is equal to 6.022 x 10²³ particles, also known as the Avogadro’s constant. These particles can be any type of species, e.g atoms, molecules, electrons, protons, neutrons, etc. In fact, if we have a which contains approximately 6.022 x 10²³ almonds, it can be said that we have 1 mole of almonds in that particular box.

This number, 6.022 x 10²³ (Avogadro’s constant) is actually defined based on the number of atoms present in 12g of ¹²C isotope of Carbon. Where 12gm is the molar mass of ¹²C or in other words the mass of 1 mole or 6.022 x 10²³atoms of 12C isotope of Carbon. 

What is the Mole Concept: Understanding the Number of Moles 

The mole concept is a simpler method for expressing the amount of a substance in chemical substances. For this, we have two steps, the first is the numerical magnitude and the other is the units in which the magnitude is expressed.

Now, let us say that the mass of a bucket is 5 kilograms, here 5” is the magnitude and the unit is ‘kilogram’. However, while dealing with the particles at an atomic or molecular level, we do not find this traditional method suitable. Like even one gram of a pure element comprises a huge number of atoms, which is the reason we are using the mole concept.

Here, the mole concept mainly focuses on the unit ‘mole’. This concept pertains to the count of a very large number of particles. Here, one mole of any substance equals the Avogadro number. The Avogadro number has a value of 6.023×10²³. This value is very  useful for measuring the products in any chemical reaction.  Thus  6.023×10²³ of atoms, molecules or particles are 1 mol of atoms, molecules or particles.

Formula for the Number of Moles Calculation

Now, in order to calculate the number of moles of any substance present in the sample, we simply divide the given weight of the substance by its molar mass.

The number of moles formula is:

[ n= frac{text{mass of substance}}{text{mass of one mole}} ]

Mathematically,

[ n = frac{m}{M}]

Here,

n = The number of moles,

m = The given mass, and

M = The molar mass

Solved Example on the Number of Moles of a Substance

Example 1: How many moles are in 25.0 grams of water?

Solution: 

In order to find the number of moles, we will have to use the following formula:

n = m/M

Molar Mass, M, of H₂O = 18.0 g/mol

Given mass, m, of H₂O = 25.0 gm

So, n = 25.0 (gm) / 18.0 (gm/mol)

Number of moles, n = 1.39 mol

Example 2: How many moles are in 3.4 x 10²³ molecules of H₂SO₄?

Options:

(a) 0.82 moles

(b) 0.01 moles

(c) 5.56 moles

(d) 0.56 moles

Answer: (d)

Solution:

1 mole of anything = 6.022x 10²³ of anything

In order to find the number of moles here, we will have to divide the given number of particles by Avogadro’s constant.

So, n = 3.4 x 10²³ / 6.022 x 10²³

Then number of moles, n = 0.56 moles

Chemistry is concerned with the process through which subatomic particles combine to form atoms. Bond order is critical in molecular orbital theory for determining bond strength and is also used in valence bond theory. 

The bond order of a molecule is a measure of the number of electrons participating in bonds between two atoms. It is used to determine the stability of a connection. 

Concept of Bond Order

The bond order concept was first introduced by Linus Pauling. The disparity between the number of bonds and antibonds is what defines it.

The bond number is the number of electron pairs that exist between two atoms. The higher the bond order, the more powerful the bond. 

Bond order is often sufficient for the number of bonds between two atoms. There are exceptions when a molecule comprises antibonding orbitals.

It is the measure of the stability of the molecule. The stability of the molecule also depends on the type of bonds. The electronic configuration of the atoms determines the bond order. There is a well-established bond order formula to calculate bond order. It is important to study the formula to find bond order to look into the structure of different compounds and calculate their stability. Let us learn more about bond orders in this chapter.

The bond order of a single covalent bond between two atoms is one, a double bond is two, a triple bond is three, and so on.

Follow these methods to discover the bond order between two covalently bonded atoms:

Create a Lewis structure.

Determine the nature of the bonds that exist between the two atoms.

0: No bond exists.

1: Single bond

2: double bond

3: triple bond

The molecule cannot form if the bond order is zero. Higher bond orders suggest that the new molecule will be more stable.

The bond order in molecules with resonance bonding does not have to be an integer.

Bond Formula – Structure

The average bond order formula considers the number of electrons on the bonding and the antibonding orbitals. It is defined as half of the difference between them. The bond order equation is

Bond order =[frac{1}{2}[N_{b}-N_{a}]]

Where Nb is the number of electrons in the bonding orbitals

And Na is the number of electrons in the antibonding orbitals.

A simpler way to find the bond order is to calculate the number of bonds between the atoms. For example, for N≡N, the bond order is 3.  

Bond Order – Reaction

How is a Bond Order Determined in a Chemical Reaction?

In a chemical reaction between two atoms, the bond order is determined by the number of electrons participating in bond formation. The atoms can interact to form covalent or ionic bonds. In Ionic bonds, electrons are transferred from one atom to another. Covalent bonds involve the sharing of electrons between two atoms. 

The electronic configuration of the atoms determines the bond order. For example, in a Carbon molecule, four bonds are shared between the two carbon atoms. Both the carbon atoms require four electrons to complete their octet. Therefore, the bond order in a carbon molecule is 4. Similarly, the bond order for nitrogen molecules is 3 and oxygen is 2.

Example:

The s shell of hydrogen atoms has one electron, and the s shell can accommodate two electrons. 

When two hydrogen atoms form a bond, each completes the other’s shell. There are two bonding orbitals generated. 

There are no electrons compelled to migrate to the next higher orbital, the p shell, resulting in the formation of antibonding orbitals. 

The bonding order = Display style (2-0)/2 = 1, is the bonding order. Hence, the molecule H₂ (hydrogen gas) is formed as a result of this reaction.

What is the Importance of Bond Order?

It is important to study the bond order formula in chemistry. It helps us to understand several factors contributing to the formation of the compound. Some of them are:

Bond order helps us to know the number of participating electrons in the formation of bonds.

• Bond order helps us to understand the stability of the bond. Higher bond order confers more stability.

• Bond order helps us to understand the bond length.

• Bond order helps us to understand bond strength. Higher bond order implies more energy is required to break the bond.

• Bond order gives us an indication of the hybridization of the molecule.

• A fractional bond order value implies that no bond is formed.

Conclusion

The concept of bond order has been studied for several years. Bond order is determined by the number of bonding and antibonding electrons. People use the bond order formula to find out the bond. Various properties of the bond can be known from bond order values.

Helium is an element that is non-toxic and non-combustible. This element is symbolized as He which is also the Helium gas chemical formula. It has an atomic number 2. It is the first noble gas in the periodic table, that is, it is an inert gas. This monatomic gas is colourless, odourless, and tasteless. It was the very first gas that was detected in the sun and has varied uses in various fields. Helium is the second lightest and second most abundant element in the whole universe after hydrogen.

Helium Gas Molecular Formula

The molecular formula of helium gas is He. It mostly exists in a monatomic state. It has an electronic configuration 1s2. The structure of helium gas is a closed-packed crystal structure. Helium belongs to group 18, period 1. When exposed to the electric field, it displays a red-orange colour. 

The Helium Formula is not written as He2 as per the Molecular Orbital Theory. However, the Helium gas formula He2 holds true at times as in the liquid phase it has some Van Der-Waal force between them becomes dominant. Liquid helium does not solidify at normal pressure irrespective of the temperature.

Properties of Helium

The properties of Helium gas is as follows:

• The Molecular weight of Helium is 4.003 g/mol.

• The density of Helium is 0.1786 g/L. It is about one-seventh as dense as air.

• It is the lightest noble gas.

• It is chemically inert.

• It has a very low viscosity.

• Helium is a tasteless, odourless, and colourless gas.

• Helium chemical formula is He.

Helium, in general, due to its inert nature, does not form any chemical compounds in normal conditions but under special conditions of pressure and temperature, helium forms certain compounds like Helium oxide. The helium oxide formula can be written as HeO. It is often mashed with hydrogen to produce water and Helium gas or with carbon to produce carbon dioxide.

Helium is a very vital gas in the whole universe and finds numerous applications in several fields. It is essential for students to be well versed in its chemical properties. 

Equivalent conductivity is the conductance of a volume of solution containing one equivalent of an electrolyte. It is denoted by the symbol ∧

Consider the volume of a V cm3 solution having one electrolyte equivalent. It has the same conductance as comparable conductance.

Specific conductance is the conductance exhibited by a 1 cm3 solution containing this electrolyte (between two electrodes with a cross-sectional area of 1 cm2 separated by a distance of 1 cm). Here, we will define equivalent conductivity in detail.

Equivalent Conductance Definition in Mathematical Terms 

Equivalent conductance definition and formula in mathematical terms:

the conductance of V cm3 ——— Λ

the conductance of 1 cm3 ——— κ

Therefore:

Λ = κ.V  ———- equation (3)

We know that the normality (N) of a solution is given by the equation below

N = n/V 1000

Equivalent conductance formula: 

V = 1000/n

For the above electrolytic solution, no. of equivalents, n = 1.

V = K x 1000/n

Hence,

relation between V and N

Equivalent conductance can be written as 

Λ = k x V

Units of Λ: units of equivalent conductance

m2 . ohm-1. equiv-1 = cm2 . mho. equiv-1

or 

m2 . Siemens. Equiv-1

Conductors and Insulators

Materials that allow easy and hindrance-free flow of electrons from one element to another are called conductors. Conductors have electric charges inside them in the form of electrons which makes it easy for the electrons to move freely.

On the other hand, insulators are the type of materials that do not allow for easy flow of the electrons from one element to another by causing hindrance. Any amount of charge that is passed through insulators only remains at the starting point where the materials meet and do not get spread across the material.

Calculation of conductance

We have established that the conductance of a solution is indirectly proportional to the resistance that it poses. Hence, conductance can be determined through finding out the resistivity of the solution being concentrated.

Since, k conductivity is reciprocal of p resistivity we can say that-

k = 1/p and p = R(a/l)

therefore, k = 1/R(l/a) or k = G(l/a)

In the above, G = cell conductance, l = the distance by which two electrodes are separated having acm2 as cross section area, l/a = cell constant which is represented by cm-1.

The conductance can be calculated after knowing the value of cell constant and solution conductance as,

k = G x cell constant

or conductivity = conductance x cell constant.

The electrolytic or ionic conductivity depends on the following factors:

• The properties of the electrolyte which is added in the solution.

• The size of the ions that are produced in the process and their solvation capacity.

• The properties of the solvent and its resistance to change shape or mobility (viscosity).

• The electrolyte’s concentration in the solution

• Temperature at which the solution is being made

Equivalent conductance at infinite dilution

When ionization increases, that is the number of ions in a solution increases, the value of equivalent conductance also increases as the solution dilutes.

For instance, at a constant temperature if we take respective concentrations of two different solutions, the solution with strong electrolyte (a greater number of ions) has a greater conductance than the solution with weak electrolyte (comparatively a smaller number of ions). However, there is an end after which more dilution in either or both of the solutions is not possible, which means it has not even the slightest effect on the concentration of the solution. This whole concept where dilution ends is called the infinite dilution.

Thus, infinite dilution can be defined as the state at which no further concentration can be obtained with any amount of dilution in a solution, as it already contains the maximum quantity of solvent possible. All the ions are completely dissociated at this state of infinite dilution.

Further information on the question of Infinite Dilution can be found here.

Kohlrausch’s Law

The state of infinite dilution can be understood by Kohlrausch’s Law. This law states that the sum of the equivalent conductance of all the anions and the cations that are present in any solution is equal to the equivalent conductance of an electrolyte at the state of infinite dilution of the same solution. Let’s assume, for instance, that salt is being dissolved in water, then the conductivity of the solution can be obtained by finding the sum of the conductance of its cations and anions in the solution.

To know more about the uses or application refer to Kohlrausch’s Law at .

Molar Conductivity

Molar conductivity is the conductance of a solution containing one mole of electrolyte or a function of a solution’s ionic strength or salt concentration. As a result, it is not a constant.

In other words, molar conductivity is the total conducting power of all the ions generated when a mole of electrolytes is dissolved in a solution. Molar conductivity is a feature of an electrolyte solution that is primarily used to determine an electrolyte’s efficiency in conducting electricity in a solution. As a result, it is not a constant.

Molar Conductivity Formula

The expression used to represent molar conductivity mathematically is given below.

μ = K / C 

μ = K / C  = K / C 

K is the specific conductivity, while c is the mole per liter concentration.

The molar conductivity of an electrolytic solution is defined as the conductance of a volume of solution containing a unit mole of electrolyte put between two electrodes of unit area cross-section. The molar conductivity unit is Sm2mol-1.

Relation Between Equivalent Conductance Formula and Molar Conductance

The relation between equivalent conductance and molar conductance can be given by:

 μ = Λ x equivalent factor of an electrolyte

The total charge on either anions or cations present in one formula unit of the electrolyte is usually the equivalent factor. In the case of acids, it can be equal to basicity, while in the case of bases, it can be equal to acidity.

Formul
a for Equivalent Conductivity and How is it Different from the Molar Conductivity Formula

The conductance of all the ions produced by one gram equivalent of an electrolyte in a given solution is known as equivalent conductance.

k V = equivalent conductance

Where V is the volume in mL that contains 1 g of electrolyte equivalent.

Molar conductance is the total conductance of all the ions produced by ionization of 1 g mole of an electrolyte in V mL of solution.. It is denoted by the symbol l.

Molar conductance = kV

Where V is the volume in mL of the electrolyte having 1 g mole. If c is the solution’s concentration.

Formula 

Equivalent conductance= Molar conductance/n

Factors Affecting Equivalent Conductivity

1. Temperature: Because the extent of ionization increases with increasing temperature, the conductance of an electrolyte solution increases.

2. Strong electrolytes undergo complete ionization and so have larger conductivities because they produce a greater number of ions.

3. Weak electrolytes, on the other hand, undergo partial ionization and so have poor conductivities in their solutions.

4. Ionic size and mobility: As the size of an ion increases, its mobility reduces, and its conductivity lowers as well.

5. Ionic mobility is diminished in more viscous solvents due to the nature of the solvent and its viscosity. As a result, the conductivity decreases.

6. As the number of ions per unit volume grows, the specific conductance increases with the increase in solution concentration.

7. However, because the extent of ionization increases with decreasing concentration (i.e. dilution), both the equivalent conductivity and molar conductance increase.

Solved Example: 

Calculation of molar conductivity of KCl solution

Given: 

Molarity (M) = 0.30M

Conductivity at 298 K (k) = 0.023 S cm–

Solution:

Molar conductivity = (1000 × k) /M

= (1000 × 0.023) / 0.30

= 76.66 cm² mol⁻¹

 So molar conductivity of KCl solution is 76.66 cm² mol⁻¹.

Conclusion 

The conductivity of a volume of solution containing one equivalent of an electrolyte is called equivalent conductivity. The conductance property of a solution containing one mole of electrolyte, or a function of a solution’s ionic strength or salt concentration, is known as molar conductivity. As a result, it isn’t always the same. In other words, when a mole of electrolyte is dissolved in a solution, molar conductivity is the total conducting power of all the ions created.

Equivalent conductance= Molar conductance/n